Store FP instead of SP in the exit info when transitioning from Dart to C++.

Store FP instead of SP in the exit info when transitioning from Dart to C++.

The exit frame info should contain the FP, not SP. This only worked so
far because FP == SP in the three exit-stubs affected
(CallToRuntime-, CallNativeCFunction-, CallBootstrapCFunction-stub).

This change has no performance implications but allows to set up a general
frame (frame size > 0) in those stubs if needed.

BUG=
R=srdjan@google.com

Committed: https://github.com/dart-lang/sdk/commit/d7c38331634bcbc8664138aea3fe1d77352bc945

[Florian Schneider, 2015-05-19 12:05:21]

fschneider@google.com changed reviewers:
+ srdjan@google.com

[srdjan, 2015-05-19 14:58:19]

lgtm

[Cutch, 2015-05-19 15:35:10]

On 2015/05/19 14:58:19, srdjan wrote:
> lgtm

What kind of frame are you planning on setting up?

[Florian Schneider, 2015-05-19 15:51:00]

On 2015/05/19 15:35:10, Cutch wrote:
> On 2015/05/19 14:58:19, srdjan wrote:
> > lgtm
> 
> What kind of frame are you planning on setting up?

For example a regular stub frame with the object saved pool pointer.

[Florian Schneider, 2015-05-20 08:23:16]

Committed patchset #1 (id:1) manually as
d7c38331634bcbc8664138aea3fe1d77352bc945 (presubmit successful).